Hi,
The error you are facing when deleting the domain from the control panel interface is due to the fact that it doesn't exist on the server physically, but only present within the
PSA database. This PSA database stores details of clients, domains, email accounts, ftp and database users in plain text format. So it's easy to correct the problem by removing the unnecessary/stale records from the Plesk database.
Backing up the database prior to any changes is strictly recommended!
If you can provide us the login details of your server, we can have this sorted out for you quickly